Galerucella calmariensis and Galerucella pusilla
The scientic names above are the two species of leaf feeding beetles that have been imported and are being released across North America. They are in the family Chrysomelidae and are very difficult to tell apart. Both share the generalized life cycle shown below.
Fall and Winter
Fall and winter are spent in the adult stage in a form of inactivity in insects known as diapause. Adult beetles borrow into the duff layer of the habitat in mid to late summer (August - early September) where they remain in diapause until spring. It is thought that they experience high mortality during this period.
Early Spring
Adults emerge in May and begin to feed on young leaves. After about 1-2 weeks of feeding, mating takes place and egg laying begins.
Late Spring and Early Summer
Eggs are often laid in the axils of leaves (photo at right) or out on the leaf surface as seen in the picture to the right. After hatching the first instar larvae move to growing tips where they crawl in between the tiny paired terminal leaves and begin to feed.
The larvae soon outgrow the enclosed space between the two tiny terminal leaves and move out and begin to feed on the surface of leaves. What has happened inside the terminal leaf pair is that the larva has eaten the growing point and this stem of the plant will no longer grow. What usually happens is that lateral buds begin to elongate, unless other first instar larvae have managed to feed on them as well.
The picture on the left shows a tip that has been damaged and will no longer elongate or set flowers later in the summer.
Summer
During the summer, it is possible to find both adults and larvae on plants in the field. The larvae shown are just about fully grown. When mature, they move down the stem and pupate in the duff layer.
Late Summer Adult Feeding
Depending on temperature, the new adults emerge after a couple of weeks. They spend a few weeks feeding actively on leaves. The picture to the left shows typical adult feeding damage with holes chewed completely through the leaf. After feeding and storing up fat reserves, the adults move to the duff layer of the soil where they remain in diapause until the following spring.
Even though these two species have only one generation a year their impact on purple loosestrife occurs throughout the season, first through adult feeding after spring emergence from diapause, second destruction of the meristems by first instar larvae, third surface feeding on the leaves by 2nd, 3rd and 4th instar larvae and last heavy feeding in late summer by adults to build up fat body needed for overwintering.
Information on this page maintained by David Voegtlin.